A shock mount that has been used in the automotive industry for securing and supporting the body or cab of a vehicle on its frame comprises two mating rings of elastically resilient material between which a body mounting part such as an ear protruding from the vehicle is engaged and clamped by a two-part spool that is seated on the vehicle frame and fixed to it by a threaded fastener. The spool parts have flanges which bear against the opposite sides of the mating rings and are threaded together so that by turning one spool part relative to the other the elastic rings and the body mounting part between them are clamped tightly between the flanges. One of the spool parts is a tubular spacer having an annular flange integral with a deep drawn tube that is internally left hand threaded. The other spool part is a thimble having an annular flange integral with a deep drawn tube that is externally left-hand threaded to fit inside and engage its thread with the screw thread of the tubular spacer. A torque nut is welded to the outer face of the thimble flange.
The mating elastic rings of the prior art are provided with an oblong projection and an oblong cavity so that they may be mated only when the projection and cavity are properly aligned.
This known shock mount is assembled by inserting the spacer tube through the center of one of the mating elastic rings, and through an opening in the body mounting part. The second mating elastic ring is then fitted over the end of the spacer tube. The end of the thimble tube is placed in the end of the spacer tube, and the thimble is turned to thread it into the spacer tube and clamp the elastic rings tightly together on the body mounting part. Then, the spool assembly and body part is seated in place on the vehicle frame, and the threaded fastener is passed up through an opening in the frame, through the tubes and the assembled spool parts, and is threaded into the nut welded onto the thimble until the entire assembly is fixed securely to the frame.
It has been found that several practical drawbacks impeded effective fastening by the prior art assembly.
During production line assembly of the spool parts crossing and jamming of the left-hand thread can and sometimes does occur, preventing the assembly from clamping together properly. An additional drawback of the known assembly becomes apparent if cross-threading of the threaded fastener and the welded nut occurs, because torque applied to the fastener in an attempt to unscrew the threaded fastener can instead cause the left-hand threaded thimble to unscrew from the spacer, jamming the entire assembly so that the unit must be cut off. The jamming and cross-threading can slow or stop the production line, increasing manufacturing cost.
The problems associated with this known shock mount have been addressed in U.S. Pat. No. 4,720,075, issued Jan. 19, 1988, and in U.S. Pat. No. 4,783,039, issued Nov. 8, 1988, and U.S. Pat. No. 4,921,203, issued May 1, 1990 (the disclosure of which is hereby incorporated by reference).
These patents disclose a two-part telescoping spool including a spacer and a thimble. Two mating resilient rings are mounted on each of the spacer and thimble, and the support part of a vehicle frame is disposed between these rings. A carriage bolt engages the thimble and allows the simultaneous securing of a body mounting part and clamping of the support part. The thimble and the spacer have mutually engaging means for limiting rotation of either of them relative to the other. Preferably, the spacer tube is formed at its axial end opposite the spacer flange into a polygon, as viewed in cross-section. The thimble tube is formed at the tube shoulder adjacent the thimble flange into a complementary polygonal shape, so that the thimble polygon formation can be received in the spacer polygon formation, preventing rotation of the two members relative to each other. The two-part spool further includes means on the inside of the spacer member for engaging an end portion of the thimble member for resisting separation of the spacer and thimble members when the thimble tube is received in the spacer tube. The engaging means disclosed in U.S. Pat. Nos. 4,720,075 and 4,783,039 comprises a plurality of inward protrusions, which is disclosed as a six tooth washer, located inside the spacer tube so that the teeth engage an enlarged end of the thimble tube. U.S. Pat. No. 4,921,203 disclosed an engaging means which comprises alternating longer aligning tabs and shorter retaining tabs.
Another known shock mount, disclosed in U.S. Pat. No. 3,218,101, issued Nov. 16, 1965, uses an interfitting thimble and spacer without means for preventing rotation of the two members, and in which the thimble can be retained in the spacer by a sleeve located between the outer walls of the thimble and the inner walls of the spacer. The sleeve frictionally mounts to the outer walls of the thimble and has detent tongues that impinge on the inner walls of the spacer to resist separation. This approach does not provide of sufficient force to resist separation of the thimble and spacer in accordance with most automobile manufacturers'current specifications.
In this respect, most automobile manufacturers have a preference for shock mounts using the telescoping, interfitted thimble and spacer (as described above in connection with U.S. Pat. Nos. 3,218,101; 4,720,075; and 4,783,039) instead of a threaded device as described in this application. Such manufacturers typically specify that shock mounts supplied to them have a minimal insertion force and a higher separation force. In other words, the thimble should be able to be inserted into the spacer with a low insertion force (to minimize assembly worker injuries from repetitive motion) but a significantly higher separation force (to insure that the thimble and spacer, once fitted together, remain assembled together with the annular rings and the body part therebetween, so as to keep the components together until the vehicle body is bolted to the frame using the carriage bolt). A typical requirement for insertion force is 40 lbs., and a typical request for separation force is 360 lbs.
As noted above, the device disclosed in U.S. Pat. No. 3,218,101 does not meet such requirements, as it provides a design in which the separation force is higher, but not significantly higher than the insertion force.
One method and device used in the industry to meet the requirements for insertion and separation force is an interfitting thimble and spacer, without means for preventing rotation of the thimble relative to the spacer. In such devices, the thimble may have a straight tube and flange, and the spacer may have an inwardly extending lip. After the thimble and spacer are fitted together, a special tool is used to deform the thimble tube and to create a knob end which is larger than the diameter of the space within the inwardly extending lip of the spacer, to prevent separation of the thimble and spacer. This approach is relatively time-consuming and complicated.
The present invention is therefore directed to an improved retainer for retaining together a spacer and thimble in a shock mount, which can be used in shock mounts in which the thimble and spacer both have, or do not have, an antirotation feature.